1. Field of the Invention
The present invention relates to a carrier impregnated with ion-specific liquid extractants, and a metal recovery process utilizing said impregnated carrier.
2. Description of the Prior Art
The concept of using porous resins as polymeric carriers for ion-specific liquid extractants has been known since the early 1970s. See S. Afr. Patent Application No. 5637 (1971), and A. Warshawsky, 83 Trans. Inst. Min. Metal. C101 (1974)["Warshawsky I."]. Typical concerns associated with using such solvent-impregnated resins include: 1) the possibility of solubility losses of the entrapped solvent; 2) the limitations of mass transfer due to limited interfacial contact with the treatment stream; and 3) the characteristics of the basic pore structure of the polymeric support. See A. Warshawsky, Ion Exchange and Solvent Extraction, Ch. 3, p. 229 (New York, 1981)["Warshawsky II."].
More specifically, the average pore diameter of suitable resins should be large enough to accommodate the organic extractant-complex, but not so large as to subject the immobilized extractant to excessive loss at elevated hydrodynamic pressure. Such resins should also exhibit little to no shrinking or swelling upon exposure to solutions of very different pH values and salt concentrations, which is a shortcoming associated with known resins such as styrenic polymer resins and stryene-divinylbenzene crosslinked resins. See Warshawsky II. at 229. Although solubility losses may be minimized by careful selection of extractants and diluents, the choice of the polymeric support plays the ultimate role in determining the commercial viability of a solvent/resin system.
Hydrometallurgy, the extraction of metals from aqueous solution, is a process that is gaining in importance as the quality of available metal-bearing ores in the world declines. See D. S. Flett, 83 Trans. Inst. Min. Metal., C30 (1974). In order to selectively extract metal ions from aqueous ore leachates, commercial hydrometallurgical operations currently utilize liquid-liquid (solvent extraction) processes. In general, these processes typically consist of a multi-stage mixer-settler section wherein the metal-bearing leachate is emulsified with an immiscible organic extractant. The organic and aqueous phases are then allowed to separate and the organic phase, now containing the extracted metal, is transferred to a stripping section in which the metal value is recovered for subsequent purification. These solvent extraction processes have several inherent limitations: (1) large capital investment is required for plant construction, (2) large losses of organic reagents are incurred by evaporation into the atmosphere, by entrainment due to poor phase separation, and by solubility of organic extractants in the aqueous phase, (3) phase separation is difficult or impossible at lower operating temperatures, and (4) relatively large equipment footprint is required.
It would be desirable to provide an improved, environmentally safe, metal extractive composition that exhibits not only a higher dimensional stability in various solvents but also has improved porosity characteristics to accommodate the needs of metal recovery applications. It would also be desirable to provide an economical, environmentally safe metal recovery process which maximizes the mass transfer contact area between the treatment stream and the extractant.